Film producers have to balance A) the processability, which determines the maximum achievable output per film extrusion machine in order to reduce manufacturing costs; B) the mechanical strength such as the impact strength to make stronger films for a given thickness and reduce the overall consumption of polymer for a given performance, and C) the optical properties such as haze.
Films made from conventional Ziegler-Natta catalyzed linear low density polyethylenes (znLLDPE) are known to have favorable physical properties such as high tensile strength. Films prepared from metallocene catalyzed linear low density polyethylenes (mLLDPE) exhibit improved tensile strength and puncture resistance, as well as improved impact resistance. Thus, the film industry has sought a polyethylene film that exhibits favorable properties similar to, or better than, those of films prepared with znLLDPE while maintaining the advantages of mLLDPE.
While the prior art may describe processes and polymers using certain linear ethylene-α-olefin copolymers, none describe multi-layer films having a dart impact (ASTM D1709) of greater than 10 g/μm and a Haze (ASTM D1003 method B) of less than 10%. Single layer blown films having an improved dart impact (over comparable films made from mLLDPE) are disclosed in U.S. Pat. No. 6,956,088. Provided herein are multilayer blown films having an improved balance of properties, in particular, improved impact resistance when compared to current LLDPEs with comparable or higher clarity.